As a detector that enables high-sensitivity detection of charged particles such as ions and electrons, for example, a charged-particle detector provided with a multiplier means such as MCP for obtaining a certain gain is known. The charged-particle detector like this is generally installed as measurement equipment in a vacuum chamber of, for example, a mass analyzer.
FIG. 1A shows a rough configuration of a residual gas analyzer (RGA: Residual Gas Analyzer) as an example of the mass analyzer. In the residual gas analyzer 1, as shown in FIG. 1A, an ion source 10, converging lenses 20, a mass analyzing part 30, and a measuring part 100 are disposed in a vacuum chamber, which is maintained at a certain vacuum degree.
In the residual gas analyzer 1, a residual gas introduced to the ion source 10 is ionized when the gas collides with thermal electrons emitted from high-temperature filaments. The ions generated in the ion source 10 in this manner are accelerated and converged when the ions pass through the converging lenses 20 including a plurality of electrodes, and, at the same time, the ions are guided to the mass analyzing part 30. The mass analyzing part 30 sorts the ions which have mutually different masses by applying direct-current voltages and alternating-current voltages to four cylindrical electrodes (quadruple). More specifically, the mass analyzing part 30 can change the voltages applied to the four cylindrical electrodes and, as a result, cause the ions having the mass-to-charge ratios corresponding to the values thereof to selectively pass therethrough. The measuring part 100 detects, as a signal (ion current), the ions which have passed through the mass analyzing part 30 among the ions introduced to the mass analyzing part 30 in the above described manner. The ion current is proportional to the amount (partial pressure) of the residual gas.
As the measuring part 100, for example, a charged-particle detector 100A provided with a MCP unit 200 for obtaining a certain gain as shown in FIG. 1B can be applied. Note that the MCP unit 200 has an input surface 200a and an output surface 200b and includes two MCPs 210 and 220 disposed in a state in which the MCPs are stacked in the space between the input surface 200a and the output surface 200b. The charged-particle detector 100A is provided with the MCP unit 200 for obtaining such a desired gain and an anode electrode 240 for capturing the electrons emitted from the output surface 200b of the MCP unit 200. Note that voltages (each of which is a negative voltage) having mutually different values are applied from a voltage control circuit (bleeder circuit) 230 to the input surface 200a and the output surface 200b of the MCP unit 200, respectively, so that the potential of the output surface 200b becomes higher than the potential of the input surface 200a. On the other hand, the anode electrode 240 is set to a ground potential (0 V), and the electrons, which are captured by the anode electrode 240 and from the MCP unit 200, are input to an amplifier 250 as an electric signal. Then, the electric signal (amplified signal) amplified by the amplifier 250 is detected from an output end OUT.